1. Field of the Invention
The present invention relates generally to a TV camera lens, and more particularly to a drive controlling technique of a TV camera lens, in which a master lens group moves forward and backward along the optical axis to adjust the flange back length and set the optical system for the macro-shooting.
2. Description of Related Art
In a zoom lens applied in a broadcast TV camera, a master lens group of a taking lens system is moved forward and backward along the optical axis to adjust the flange back length, thereby forming a sharp image of an object on a picture screen. Japanese Patent Publication Nos. 58-1401 and 60-46405 disclose TV camera lenses in which the master lens group is moved forward and backward along the optical axis to set the optical system for the macro-shooting.
That is, a rotary adjustment knob is usually provided at one side of the mount frame (the right side viewed from the front, i.e. the left side of a user) so that rotational force of the adjustment knob can be transmitted to a master lens driving mechanism in a lens mount via a power transmission mechanism such as an assembly of gears. If the user turns the adjustment knob by hand, an image formation position of the TV camera lens can be fine adjusted and the macro-shooting can be performed.
In the TV camera lens in which the master lens group is moved to perform both the flange back length adjustment and the macro-shooting, however, since the normal shooting is usually performed after the flange back length adjustment is completed, and the macro-shooting is performed as the need arises during the normal shooting, it is difficult to correctly return the master lens group to the initially-adjusted position of the proper flange back length when the shooting is switched from the macro-shooting to the normal shooting.
In a well-established technique, the master lens group is moved for the purpose of achieving special effects such as obscuring a shot image. In the conventional TV camera lens, however, since the master lens group is moved with the rotation of the adjustment knob provided at the side of the casing and the rotational force is mechanically transmitted via the assembly of gears or the like, it is difficult to smoothly move the master lens group and naturally obscure the shot image.